FIELD OF THE INVENTION
The invention relates to an optical device, which is also called an optical encoder, for quantitative detection of linear and rotary movements. The optical device contains a light emission device, a grid device containing translucent areas and opaque areas, a detection device and an evaluation circuit coupled to the detection device.
Optical encoders are used to detect the rotation angle or, respectively, a length and a direction of a rotary movement or, respectively, linear movement of moving bodies. The essential components of such a device are the emitter system, a grid plate, normally a grid disk or a grid straight edge, and the detector system. The emitter system normally contains a light-emitting diode. The light beam emitted from the laser diode is modulated by the grid plate. The grid plate is connected to a moving body and has a periodic opening pattern. The detector system detects the transmitter signal (modulated by the grid plate) from the laser diode and, at the output, and supplies information relating to the light beam and the direction of movement.
Previous versions of optical encoders contain a light-emitting diode having additional optics, the grid plate and a detector array with evaluation logic. At the emitter end, a light beam is produced, which illuminates the detector array as uniformly as possible. The detector array contains at least two photodiodes, which are disposed in the direction of a linear movement, or tangentially with respect to a rotary movement. The distance between the photodiodes is one quarter of the grid disk period, and the signals from two adjacent photodiodes are phase-shifted through 90.degree. with respect to one another. The output signals from the photodiodes are suitably processed in an evaluation circuit in order to supply the position and direction of movement.
Two photodiodes disposed in a line are sufficient to define the position and direction. However, embodiments having four photodiodes disposed in a line are widely used in the prior art, for example as described in U.S. Pat. No. 4,654,525. This configuration and the evaluation circuit which is coupled to the photodiodes additionally allow compensation for light intensity fluctuations in the laser diode.
The previous systems are thus limited to a configuration of a plurality of photo receivers on the detector side. Such a limitation may be disadvantageous for several reasons. It is thus of primary importance for an optical encoder to be constructed in a space-saving manner. This requirement is thus difficult to satisfy from the start on the detector side.